Abstract
High fuel-injection pressures and high EGR rates are strategies for reducing soot and NOx for diesel engines. These two emission-reduction methods are interdependent and tradeoffs must be evaluated. High fuel-injection pressure results in smaller soot particles, which lowers mass-based soot emission. High EGR rates increase the carbon content in the cylinder charge, which tends to enhance soot precursors formation during combustion. Smaller soot particles with a higher number density within the EGR gas favor formation of thermophoretic deposit in the EGR cooler. Increased deposit thickness on the heat transfer surfaces leads to decrease in the effectiveness and increase in the flow resistance of the EGR cooler. Consequently, deterioration in the EGR-cooler performance as a result of cooler fouling has a significant impact on engine-out NOx emissions. This study reviews the physics for the EGR cooler fouling process, characteristics of the soot deposit in the EGR cooler. Interdependence of the emission-reduction methods and their impacts on the EGR cooler fouling, and characterization of the performance of fouled EGR coolers are also discussed.
